The melting of iron ore by a reducing gas generated in a furnace and the subsequent recovery of the reducing gas generally includes burning coke using hot air to generate a hot gas which is then passed upwardly through a coke-filled layer to melt iron retained therewith. The by-product gas or spent gas obtained in the process is a low-calorie gas rich in N2 and CO2. More recently, coal and hydrocarbon-based fuel is gasified in the presence of oxygen and steam to form a hot gas which is passed upwardly through a coal char fluidized bed to melt semi-reduced iron, the hot gas can be recovered. These processes have drawbacks like: the by-product gas obtained is a low-calorie gas rich in N2 and CO2, and cannot be used as a reducing or fuel gas; and the coal char fluidized bed is unstable and poor in the semi-reduced iron retaining power, thus, cannot bear the semi-reduced iron on the coal-char fluidized bed for a longer period of time and the iron must be melted in the possible shortest time with a large amount of the hot gas, which means that the thermal efficiency of melting is low.
Blast furnace process, on the other hand, is advantageous in that the gas reduction of iron ore proceeds in a stable manner, and the melt has a reduced content of iron oxides, thus posing little or no problems due to erosion of refractory materials in comparison with the melting/reducing processes. In addition, the blast furnace process exhibits a very high thermal efficiency due to the fact that the gas-reduction and melting of iron ore is carried out in the same vessel, and reduces the consumption of energy if the by-product gas is recovered for other purposes. However, the blast furnace process requires the use of coke of high quality, such as with high strength or low reactivity, so as to ensure good permeability in the furnace and stable descending of the stock therein. The production of these cokes inevitably needs a feed of coking coal of high quality and high energy for coking. The agglomerated iron ore used should also have a high strength and excel in the softening properties at high temperatures.
Therefore, there is felt a need for a process for producing cast iron with the productivity and thermal efficiency similar to a blast furnace process as well as with the possibilities of applying cheaper raw materials. Some of the related prior art is listed in the following discussion.
The prior art of producing molten iron and reducing gas includes following: 1. Process of Sumitomo Metal Industries Ltd, Japan (U.S. Pat. No. 4,504,043) In a melting/gasifying furnace including a coke filled layer, coal is gasified by oxygen blown through tuyeres into a hot reducing gas which is caused to ascend through the coke filled layer so as to melt the reduced iron supported on the top of the coke filled layer. The resulting molten iron flows down through the coke filled layer and is collected in the lowermost region of the coke filled layer and discharged therefrom while the hot gas is recovered. The thus recovered gas is fed into a shaft reduction furnace to reduce the iron ores and the thus formed reduced iron is supplied into the melting/gasifying furnace. In addition to the coal a variety of fuels mainly comprising carbon and hydrogen such as heavy oil, natural gas etc. are used for gasification. The fuel is blown through the tuyeres and/or charged through middle openings disposed above the tuyeres.
2. Process of synthesis gas production using blast furnace as gasifier by Arthur G. McKee & Company, Ohio (U.S. Pat. No. 4,153,426) The furnace is charged in a conventional manner with particles of solid carbonaceous material such as normal, low grade or undersized coke together with slag-producing material, such as limestone, silica and/or basic oxygen furnace and/or open hearth furnace slag. Fluent fuel such as pulverized coal mixed with oxygen-containing gas and with lime if desired is injected into pre-ignition chambers near the hearth line of the furnace. The fluent fuel is ignited and partially gasified in the pre-ignition chambers, creating a hot reducing gas that enters the furnace raceway and passes upwardly into and through the body of charge material in the furnace stack. At the resulting high temperatures, ash from the fluent fuel liquefies within the system to provide a liquid slag. Under a controlled high temperature reducing atmosphere, the hot lime removes essentially all sulfur from the product gas. To reduce the high gas temperature, steam is injected above the pre-ignition chambers. The steam reacts with the hot solid carbonaceous material in the stack to enrich the product gas with additional hydrogen and carbon monoxide. Liquid carbonaceous material such as oil, tar, or the like may be injected into the furnace stack above the location at which steam is injected and is cracked by the sensible heat of the gas passing through the body of charge material in the furnace, thus further cooling the gas and enriching its calorific value.
The resulting product gas can be used in place of natural gas for heating purposes in steel making operations, as a gas in the production of chemicals, as a reducing gas for the metals industries, for general heating purposes, as well as for other purposes.
3. Process for producing liquid crude iron and reducing gas by Korf-Stahl AG. (U.S. Pat. No. 4,317,677)
A process for the production of molten crude iron and reduction gas is described wherein the molten iron and gas are formed in a smelting gasifier, to which is introduced at the upper portion thereof preheated sponge iron of particle size between 3 mm and 30 mm and coal to form a fluidized bed, and an oxygen-containing gas at the lower portion thereof, and controlling the ratio of oxygen-containing gas and coal to maintain a high temperature zone in the lower portion of the gasifier and a lower temperature zone in the upper portion thereof, the oxygen containing gas being introduced substantially immediately above the resulting melt which is formed at the bottom of the gasifier.
4. U.S. Patent application No. 20100064855 of Lanyi et al. teaches a method for manufacturing of steel by employing an integrated system for blast furnace iron making and power production based upon higher levels of, oxygen enrichment in the blast gas. The integrated system leads to; 1) enhanced productivity in the blast furnace, 2) more efficient power production, and 3) the potential to more economically capture and sequester carbon dioxide. Oxygen enhances the ability of coal to function as a source of carbon and to be gasified within the blast furnace thereby generating an improved fuel-containing top gas.